The present invention is directed to a disk caching technique using software, in particular, disk caching software for use on an Open VMS operating system. Open VMS is the operating system used on VAX and Alpha AXP computers.
Computer users are always looking for ways to speed up operations on their computers. One source of the drag on computer speed is the time it takes to conduct an input/output operation to the hard disk drive or other mechanical disk devices. Such devices are slowed by mechanical movement latencies and I/O bus traffic requirements. One conventional method for avoiding this speed delay is to cache frequently accessed disk data in the computer main memory. Access to this cached data in main memory is much quicker than always accessing the hard disk drive for the data. Access speed to a hard disk drive is replaced by main memory access speed to the data resident in the cache.
There is a significant down side to the conventional form of caching techniques. Caches are conventionally organised as to be made up of fixed sized areas, known as buckets, where the disk data is stored, with all the buckets added together making up the fixed total size of the computer main memory allocated for use by the cache. No matter what size the original disk access was this data has to be accommodated in the cache buckets. Thus, if the disk access size was very small compared to the cache bucket size, then most of the bucket storage area is wasted, containing no valid disk data at all. If the disk was accessed by many of these smaller accesses, then the cache buckets would get used up by these small data sizes and the cache would not apparently be able to hold as much data as was originally expected. If the disk access size was larger than the cache bucket size, either the data is not accommodated in the cache, or several cache buckets have to be used to accommodate the disk data which makes cache management very complicated. With this conventional approach to disk caching the computer user has to try to compromise with the single cache bucket size for all users on the computer system. If the computer is used for several different applications, then either the cache bucket size has to be biased to one type of application being at a disadvantage to all the other applications, or the cache bucket size has to averaged against all applications with the cache being at less an advantage as would be desired. It is an object of the present invention to reduce this down side of using a disk cache.